Volume 24,
Issue 5,
1982

The effective sealing of joints in concrete structures subjected to low heads of water, such as canals and small off-channel balancing storage reservoirs, has developed into a matter of gathering importance. This is so on account of steeply rising costs of supplying water to consumers. Pumping from storage to storage and conveying water through tunnel systems and long interlinking canals, with the more elaborate and expensive control works they have come to entail, has underlined the increasing need to ensure that seepage losses through open or inadequately sealed canal joints be minimized.

While the engineer has at his disposal a few standard specifications for joint sealants such as those based on polysulphides (whether pure or coal-tar extended), silicone rubbers and oleo-resinous mastics, nothing seems to have been done in South Africa until very recently to investigate further the merits and demerits of a family of low-cost elastomeric joint sealants which could in general be described as 'polymer coal tars', being one-pack heat-curing rubberized coal-tars.
This paper reports on some further evaluation of the practical performance of this sealant material which has very recently been developing in local manufacture and, as hinted at by its description, can have a local raw material content in excess of 95 per cent. It is a hot-pour; sealant and as such is confined in range of practical applications to joints inclined at angles no steeper than about 65o to the horizontal. Hand-screeded concrete lining of water retaining structures seldom exceeds 3 m in depth.
For the Directorate of Water Affairs of the Department of Environment Affairs, the interest, in studying the sealants' performance and practical and economic potential, fell mainly on canals. It was decided to examine, in the Directorate's laboratory, the resistance to extrusion or rupture through typical concrete lining joints under hydraulic pressure. Heads of water of up to 6 m were applied.
The information obtained in this way could serve as a useful adjunct to the physical test results obtained from the SABS laboratories when it comes toadjudicating tenders for the supply of these sealants.

It was illustrated in a recent study that a variation in the effective-length value for columns in unbraced steel frames can be responsible for a considerable difference in the design of such columns. It was also shown that such variation in effective length can easily occur when comparing results of effective-length charts with solutions obtained from a rigorous elastic buckling analysis of the entire framework.

In this investigation a number of slender columns in symmetrical and unsymmetrical unbraced reinforced concrete frames have been evaluated wing effective-length values derived from the relevant formulae of the South African Code of Practice for the Structural Use of Concrete, SABS 010W. Subsequently, the same columns were analysed using a more accurate assessment of the effective length. A comparison of the results has shown that vast differences can occur in the prediction of the load carrying capacity of certain slender columns.